Nitrate-Induced Changes in Protein Synthesis and Translation of RNA in Maize Roots

Abstract

Nitrate regulation of protein synthesis and RNA translation in maize (Zea mays L. var B73) roots was examined, using in vivo labeling with [5Sjmethionine and in vitro translation. Nitrate enhanced the synthesis ofa 31 kilodalton membrane polypeptide which was localized in a fraction enriched in tonoplast and/or endoplasmic reticulum membrane vesicles. The nitrate-enhanced synthesis was correlated with In the present study, we have searched for nitrate-inducible polypeptides in maize roots, in an attempt to identify nitrate membrane transport proteins. We have examined the profiles of polypeptides synthesized in maize roots incubated with or without nitrate. The spectra of in vitro translation products of nitrateinduced and noninduced total root RNA were also compared.MATERIALS AND METHODS Plant Material. Maize seeds (Zea mays L. var B73) were germinated in darkness at 29'C between germination paper saturated with 0.5 mM CaSO4. After 3 d, the roots ofthe seedlings were transferred to aerated solutions containing 0.5 mM CaSO4, 5 mM K2HPO4, 1 mM MgSO4, 1.25 mM K2SO4, micronutrients (13) and FeEDTA at 1 mM Fe. The seedlings were grown in an incubator at 29°C under fluorescent lights (about 100-200 ,uEm-2 -s) with a light/dark cycle of 16/8 h. During induction periods, typically during the first part of the light period on the 7th d after the beginning ofgermination, the roots ofthe seedlings were transferred to aerated solutions containing, in addition to 10 mm Mes (pH 5.5), either 5 mM Ca(N03)2 (induced) or 5 mM CaCl2 (noninduced). To label root proteins, the roots of 5 to 8 seedlings were bathed in either control or induction solutions (45 ml)

Correlated Induction of Nitrate Uptake and Membrane Polypeptides in Corn Roots

“…McClure et al (22) found that nitrate treatment enhanced the synthesis of a 31 kD polypeptide in a microsomal fraction from corn roots but found no consistent differences in [35S]methionine labeled polypeptides in the plasma membrane fraction. We observed enhanced synthesis of 30 and 47 kD polypeptides in a microsomal fraction (Fig.…”

“…Competition (12) and inhibitor (8) induction of more nitrate carriers in the plasma membrane. Recently, a small (mol wt = 31,000) membrane-associated polypeptide was found to be induced by nitrate in a microsomal fraction from corn roots (22). However, it was concluded that the polypeptide might be a regulator of nitrate uptake rather than a component of a nitrate carrier.…”

Development of Accelerated Net Nitrate Uptake

“…Morgan et al (20) observed a more rapid development of accelerated nitrate uptake than in situ nitrate reduction upon initial exposures of maize seedlings to nitrate. McClure et al (19) reported enhanced 35S-methionine in vivo labeling of a 31 kD membrane polypeptide in a tonoplast-and endoplasmic reticulum-enriched fraction of 8-h 10 mm nitrate-induced roots. The labeled polypeptide appeared to turn over very slowly after removal of external nitrate (19), which would be consistent with the observed decay pattern of the accelerated nitrate uptake following nitrate deprivation (see Fig.…”

Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pH

“…Uptake of NO~ is induced by NO,~ and is an energyrequiring process which is restricted by inhibitors of RNA and protein synthesis as well as inhibitors of respiratory and oxidative phosphorylation (Haynes, 1986). Sustained RNA and protein synthesis is required for induction of enhanced NO£ uptake (MacKown, 1987;McClure et al, 1987) and low molecular weight polypeptides associated with the plasma membrane (probably part of the NO 3-transport system) have been identified that are induced by NO 3 pretreatment (Dhugga et al, 1988a;b). S.uch findings suggest that nitrate uptake depends on coupled electron flow to produce ATP and the presence of a relatively labile membrane-bound protein (Clarkson, 1986).…”